If I like it, I buy it. I love the different blenders, marbles, fusions, etc. I only buy panels if I've got a specific plan for them. Love Kaufman Kona muslin and the printed muslins.
Who do you plan to quilt for? It's good to get a variety of colors if you can. There are some colors I have very little of, such as greys or browns. Mostly I have blues, purples, greens in a variety of prints and different size designs. Don't get all the same print in a bunch of colors. You need more variety! :)